Magnetic head

Abstract: A magnetic head having a pair of magnetic cores defining a magnetic gap in-between is disclosed. The side of each magnetic core facing a recording medium is formed of a single-crystal ferrite, with the remaining portions of each magnetic core being formed of poly-crystal ferrite. The surface of the magnetic core facing the recording medium and the abutment surface of the magnetic core are the {100} plane and the {100} plane of the single-crystal ferrite, respectively. The magnetic head has excellent abrasion resistance and electro-magnetic conversion characteristics.

Description: BACKGROUND OF THE INVENTION This invention relates to a magnetic head incorporated into a magnetic recording/reproducing apparatus, such as a VTR or a data storage device. In the magnetic head, incorporated into the magnetic recording/reproducing apparatus, such as the VTR or the data storage device, a magnetic material formed of single-crystal ferrite is commonly employed as the material constituting a magnetic core. The magnetic head is made up of magnetic core halves 81, 82, facing each other via a front gap g 7 and a back gap g 8 as a boundary and abutted and bonded to each other, as shown in Fig.12. Each of the magnetic cores 81, 82 is formed of single-crystal ferrite. Track width suppression grooves 83, 84 are provided on the junction surfaces of the magnetic cores 81, 82 for restricting the track width of the magnetic gap g 7 . Fused glass 87 is charged in the fused state in the track width suppressing grooves 83, 84 for bonding the magnetic cores 81, 82 together. Coil winding slots 89, 90 and winding guide slots 91, 92 are formed on the abutment surfaces and on the lateral surfaces of the magnetic cores 81, 82 so that coils, not shown, may be placed and wound via the coil winding slots 89, 90. With the above-described magnetic heads, single-crystal ferrite is extensively used as the constituent material for the magnetic core. However, if the single-crystal ferrite is used, the ultimate magnetic head is changed significantly in abrasion resistance or electro-magnetic characteristics due to the difference in the orientation of the slicing surface. Consequently, the selection of the crystal orientation is crucial when slicing a magnetic head from an ingot of the single-crystal ferrite. For example, with the use of the Mn-Zn single-crystal ferrite, there have hitherto been known a β ferrite head having, for a surface facing the recording medium (medium facing surface), an abutting surface and a lateral surface, the planes {110}, {100} and {110}, and a J ferrite head having, for the medium facing surface, the abutting surface and the lateral surface, the {211}, {111} and {110} planes, respectively. However, the β and J ferrite heads have their own merits and demerits. That is, since the {211} plane is not satisfactory in abrasion resistance, as shown for example in Fig.13, the magnetic head formed of J ferrite has a drawback that it is not satisfactory in the abrasion resistance. On the other hand, with the magnetic heads which is extensively used in VHS system, the electro-magnetic conversion characteristics of the magnetic head formed of J ferrite are a little better than those of the magnetic head formed of β ferrite, such that it is extremely difficult to optimize the abrasion resistance and the electro-magnetic conversion characteristics simultaneously. If the surface not satisfactory in abrasion resistance is used as the medium facing surface, as with the above-described J ferrite head, it may be contemplated to increase the depth length of the magnetic gap for assuring the service life of the magnetic head product. However, if the depth length is increased, the magnetic core efficiency of the magnetic head and also the electro-magnetic conversion characteristics are lowered. Prior art document JP-A-57053818 discloses a composite magnetic head composed of two pieces of single crystal Mn-Zn ferrite that oppose to each other via a working gap. The (110) face of at least one of the two pieces of the Mn-Zn ferrite is set substantially parallel to the surface on which a magnetic pole path is formed, and at the same time an angle of 15 ∼ 40° or 95 ∼ 120° is obtained for the angle  formed by the <100> direction existing within the (110) face and the surface on which the gap is formed. On the other hand, rear magnetic circuit parts form a composite magnetic head containing the adhesion of a polycrystal Mn-Zn. The above prior art is reflected by the preamble of claim 1. Further, prior art document JP-A-3156709 discloses a magnetic head in which a magnetic core is formed of a C type core piece and I type core piece consisting of single crystal ferrite, the (110)-face of which is nearly parallel with the main magnetic path forming surface, and a magnetic thin film consisting of an Fe-Al-Si alloy formed on the I type core piece. The C type core piece and a glass part joining the I type core piece are provided in an upper part of a space for winding. The magnetic gap is formed of a gap regulating film consisting of a nonmagnetic material, such as SiO 2 . Prior art document SMPTE Journal, vol. 92, no. 12, December 1983, SCARDALE, NY, USA, pages 1274-1279, H. Tanimura et al. 'A Second Generation Type-C One-Inch VTR' (page 1276, lines 6-26), describes a magnetic head in which two materials are combined in a single head. A single and polycrystal head has a higher output, a lower scrape noise, and a higher reliability than the traditional single crystal ferrite head. The part of the head which contacts the tape is single crystal with high wear resistance, while the bulk magnetic properties are determined by the polycrystalline material. Document JP-A-54134613 discloses a magnetic head wherein a core portion is formed by a head chip opposing to a magnetic recording medium and a back core which is bonded to this head chip and constitutes one magnetic path with the head chip. The head chip 1 is constituted by single crystal ferrite and the back core by polycrystalline ferrite. Further the side face defining the track width of the head chip is set at the crystal face (110) of the single crystal ferrite or near the same and the faces opposing to a magnetic gap are set on the crystal face (100) face or (111) face or near the same of the monocrystalline ferrite. Finally, prior art document JP-A-4023210 describes a magnetic head comprising a front-magnetic gap portion made of single crystal ferrite, a core portion and a rear magnetic gap of polycrystalline ferrite. A magnetic path forming plane of the single crystal ferrite is a (110)-plane. It should be noted that a single-crystal ferrite has a cubic crystal structure. For a cubic structure, the planes (100), (010), (001), (-100), (0-10) and (00-1) are all equivalent to each other. For this reason, in the following {100} means all these planes. SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic head superior in abrasion resistance and electro-magnetic conversion characteristics and having long service life. To solve this object the present invention provides a magnetic head as specified in claim 1. Preferred embodiments of the invention are described in the subclaims. As a result of our eager searches towards accomplishing the above object, the present inventors have found that, by constituting the medium facing surface of the magnetic core by single-crystal ferrite and the remaining portion thereof by polycrystal ferrite, and by controlling the plane orientation of the single-crystal ferrite, a magnetic head having excellent abrasion resistance and electro-magnetic conversion characteristics may be produced. Thus, a magnetic head has a pair of magnetic cores abutted together for defining a magnetic gap therebetween, wherein the medium facing surface sides of the magnetic cores are formed of single-crystal ferrite and the remaining portions of the magnetic cores are formed by polycrystal ferrite, with the medium facing surface sides and the abutment surface sides of the magnetic core being the {100} plane and the {100} planes of the single-crystal ferrite, respectively. Since the {100} plane of the single-crystal ferrite is superior in abrasion resistance, the abrasion caused by the rubbing of the recording medium may be suppressed and hence the service life of the magnetic head may be prolonged by employing the {100} plane as the surface facing the recording medium. If the medium facing surface is the {100} plane, deterioration in the electro-magnetic conversion characteristics may be feared. However, since the major portions of the magnetic core are constituted by poly-crystal ferrite, the deterioration in the electro-magnetic conversion characteristics ascribable to the crystal orientation of the single-crystal ferrite disposed towards the medium facing surface may be minimized, while the rubbing noise may be simultaneously lowered. In addition, since the medium facing side of the magnetic core is the {100} plane of the single-crystal ferrite and hence is superior in abrasion resistance, it becomes possible to reduce the depth length of the magnetic gap thereby improving the core efficiency and the electro-magnetic conversion characteristics of the magnetic head. Furthermore, if the magnetic head of the present invention is loaded on a magnetic recording/reproducing apparatus, such as a VTR or a data storage device, the operating reliability of the magnetic recording/reproducing apparatus may be improved and recording may be made with a higher recording density. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a perspective view showing a magnetic head of an embodiment 1 according to the present invention. Figs.2 to 5 show the method for producing the magnetic head of the embodiment 1, step by step, where Fig.2 is a perspective view showing the step of forming a bonded ferrite block. Fig.3 is a perspective view showing the step of forming a track width suppression groove in the bonded ferrite block. Fig.4 is a perspective view showing the step of forming a winding slot and a glass slot in the bonded ferrite block. Fig.5 is a perspective view showing the step of stacking a pair of bonded ferrite blocks. Fig.6 is a perspective view showing a completed magnetic head block. Fig.7 is a perspective view showing a completed magnetic head chip block. Fig.8 is a graph showing changes in the amount of the abrasion caused in the magnetic head as plotted against the medium rubbing time for the magnetic head of the embodiment 1 and a conventional magnetic head. Fig.9 is a graph showing changes, with respect to the frequency, in the rubbing noise produced in the magnetic head of the embodiment 1 and a conventional magnetic head. Fig.10 is a perspective view showing a magnetic head of the embodiment 2 according to the present invention. Fig.11 is a perspective view showing a magnetic head of the embodiment 3 according to the present invention. Fig.12 is a perspective view showing a conventional magnetic head. Fig.13 is a graph showing abrasion resistance characteristics of the conventional magnetic head. DETAILED DESCRIPTION In magnetic recording/reproducing apparatus, such as VTR or data storage, investigations in high density recording or short wavelength recording are proceeding and, for keeping therewith, the high coercivity magnetic recording medium is being used in increasing numbers. In order to accommodate for this, a variety of magnetic heads employing magnetic metal materials have been developed. Typical of these magnetic heads are a metal-in-gap (MIG) head and a tilted sendust sputtered (TSS) head. With the MIG head, the magnetic core is made up of an oxide substrate of, for example, a single-crystal ferrite, and a magnetic metal material. A thin magnetic metal film is formed on the abutting surface of the magnetic core along its profile and the magnetic gap is formed by abutting portions of the thin magnetic metal layers. The TSS head, on the other hand, has its magnetic core similarly constituted by a substrate formed of an oxide, such as single-crystal ferrite, and a magnetic metal material. A cut-out groove is formed in the abutting surfaces of the magnetic cores and the thin magnetic films are formed at a pre-set angle on the abutting surfaces, these thin magnetic metal films being abutted together for defining the magnetic gap therebetween. The present invention may be applied to the MIG heads or the TSS heads according to the second subject-matter and the third subject-matter of the present invention, respectively. With the magnetic head of the second subject-matter of the present invention, thin magnetic metal films are formed on abutment surfaces of the magnetic cores and the magnetic gap is formed by abutting the magnetic metal films together. With the magnetic head of the third subject-matter of the present invention, a cut-out groove is formed in the abutment surfaces of the magnetic cores at a pre-set angle with respect to the abutment surfaces, and thin magnetic metal films are formed in the cut-out groove and abutted together to form the magnetic gap therebetween. PREFERRED EMBODIMENTS Referring to the drawings, preferred embodiments of the present invention will be explained in detail. Embodiment 1 The present embodiment is directed to a usual ferrite head having its magnetic core formed of ferrite. The magnetic head of the present embodiment is made up of a pair of magnetic cores 1 and 2 abutted and connected to each other with a magnetic gap g 1 (front gap) and a magnetic gap g 2 (back gap) in-between, as shown in Fig.1. Meanwhile, track width suppression grooves 3, 4 for restricting the track width of the magnetic gap g 1 and track width suppression grooves 5, 6 for restricting the track width of the magnetic gap g 2 are formed in the abutment surfaces of the magnetic cores 1 and 2. Fused glass is charged in molten state between the track width suppression grooves 3, 4 and the track width suppression grooves 5, 6 for connecting the magnetic cores 1 and 2 together. There is no limitation to the fused glass if it is such fused glass as is commonly employed for the manufacture of the magnetic heads. Coil winding slots 9, 10 and winding guide slots 11, 12 are formed in the abutting sides and in the lateral sides of the magnetic cores 1 and 2. Coils, not shown, are wound across the winding slots 11, 12 and the guide slots 9, 10. With the magnetic head of the present embodiment, the medium facing surfaces of the magnetic cores 1 and 2 are formed by single-crystal ferrites 13, 14, with the remaining portions of the magnetic cores 1 and 2 being formed of poly-crystal ferrites 15, 16. The single-crystal ferrite is sliced so that the medium facing surface is the {100} plane and the abutment surface is the {100} plane. The magnetic head of the present embodiment is fabricated by the following process steps. First, plate-shaped single-crystal ferrites 13, 17, sliced in a pre-set plane orientation, are arrayed in alternation with plate-shaped poly-crystal ferrites 15, 18 and bonded together to form a bonded ferrite block 19, as shown in Fig.2. A gap-forming surface 19a of the bonded ferrite block 19 is then polished to a mirror finish. The single-crystal ferrites 13, 17 are so set that the medium facing surfaces 13a and 17a and the abutting surfaces 13b and 17b are {100} planes and the {100} planes, respectively. Then, a plurality of track width suppression grooves 20 of arcuate cross-sectional shape, delimiting a track width T w of the magnetic gap of the magnetic head, are formed at a pre-set track pitch on the bonded ferrite block 19 at right angles to the medium facing surfaces 13a, 17a, as shown in Fig.3. That is, a land having a track width T w is formed between neighboring ones of the track width control grooves 20. Then, winding slots 9, 22 and glass slots 21, 23 are formed at right angles to the track width control grooves 20 in the bonded ferrite block 19, as shown in Fig.4. The winding slots 9, 22 are each in the form of a frustum and designed to be used for placing the coils therein. The bottom of the winding slots 9, 22 is the coil winding surface, and the distal end of the inclined surface delimits the magnetic gap depth. The winding slots 21, 23 are each in the form of a frustum and designed to be used for glass fusion in the course of a subsequent process step for assuring bonding of the bonded ferrite block 19 to another bonded ferrite block which is formed similarly to the bonded ferrite block 19. Front gap forming surfaces 24, 26 and back gap forming surfaces 25, 27 are now defined by forming the track width suppression grooves 20, winding slots 9, 22 and the glass slots 21, 23. A bonded ferrite block 28, shaped similarly to the bonded ferrite block 19, is formed by the process steps similar to those for the bonded ferrite block 19, as shown in Fig.5. The bonded ferrite blocks 19, 28 are abutted and stacked together so that the front gap forming surface 24, back gap forming surface 25, front gap forming surface 26 and the back gap forming surface 27 of the block 19 are coincident with a front gap forming surface 29, a back gap forming surface 30, a front gap forming surface 31 and a back gap forming surface 32 of the bonded ferrite block 28, respectively. A gap spacer, not shown, having a thickness corresponding to a pre-set gap length, is interposed in the abutting portions except a gap forming region. Fused glass rods, not shown, are interposed in the gap between the winding slots in the bonded ferrite blocks 19 and 28, and in the gap between the glass slots and fused with the bonded ferrite blocks 19 and 28 pressed together in order to charge the fused glass between the blocks 19, 28 to effect glass bonding. A magnetic head block 34 as shown in Fig.6 is now produced. At this time, the fused glass is charged in the track width control grooves 20, 33 for providing contact characteristics of the magnetic head with respect to the recording medium proper to the fused glass. The magnetic head block 34 is severed into a number of magnetic head chips blocks, one of which is shown at 35 in Fig.7. The medium facing surface 13a is ground to a cylindrical surface. The magnetic chip block 35 is further severed into plural magnetic head chips, and the winding guide slots 11, 12 are cut in the lateral sides of each magnetic head chip to complete the magnetic head shown in Fig.1. The magnetic head of the present embodiment, produced as described above, and a conventional β-type ferrite head, the magnetic core of which is formed of β single-crystal ferrite, were checked as to their abrasion resistance and electro-magnetic conversion characteristics. For evaluating the abrasion resistance, each magnetic head was loaded on a 8-mm VTR, and comparative measurements were made on the amounts of wear caused to the magnetic heads with respect to the rubbing time of the recording medium. The results are shown in Fig.8. The results of the magnetic head of the present embodiment and those of the conventional β ferrite magnetic head are indicated by ○ and □, respectively. It may be seen from Fig.8 that, since the medium facing surface of the present magnetic head is (100), it has excellent abrasion resistance, such that, with the medium rubbing time of 450 hours, the abrasion resistance is four times that of the conventional magnetic head. In evaluating the electro-magnetic conversion characteristics, comparative measurements were made of the rubbing noise with respect to the frequency of each magnetic head. Among the causes of the deterioration of the electro-magnetic conversion characteristics, there are possibly the plane orientation of the single-crystal ferrite of the magnetic head and the oscillations experienced by the single-crystal ferrite. With the magnetic head of the present embodiment, deterioration in the electro-magnetic characteristics due to oscillation noises caused by the oscillations experienced by the ferrite is feared, rather than that due to the plane orientation of the ferrite. With this in view, measurements were made of the rubbing noise of each magnetic head with respect to the frequency. The results are shown in Fig.9, in which A 1 , A 2 , A 3 and A 4 represent the rubbing noise of the present magnetic head, the amplifier noise of the present magnetic head, the rubbing noise of the conventional magnetic head and the amplifier noise of the conventional magnetic head, respectively. It may be seen from this that the magnetic head of the present magnetic head is lower in the rubbing noise and higher in electro-magnetic conversion characteristics than the conventional magnetic head. The reason is possibly that the major portions of the magnetic core of the magnetic head of the present embodiment is formed of poly-crystal ferrite. Consequently, with the magnetic head of the present embodiment, since the medium facing surface of the magnetic core is formed of single-crystal ferrite, with the remaining portion thereof being formed of poly-crystal ferrite, and the medium facing surface and the abutting surface of the magnetic core being the {100} and {100} of the single-crystal ferrite, there is little risk of abrasion due to the rubbing of the recording medium. On the other hand, the deterioration of the electro-magnetic conversion characteristics due to the crystal orientation of the ferrite is minimized and the rubbing noise is scarcely produced, as a result of which good abrasion resistance and superior electro-magnetic conversion characteristics may be achieved. Embodiment 2 The present embodiment is directed to the TSS head in which an inclined cut-out groove is formed in an abutment surface of the magnetic core and a thin magnetic metal film is formed at a pre-set angle with respect to the abutment surface, with a magnetic gap being formed by abutment of the thin magnetic metal films of two magnetic cores. The magnetic head of the present embodiment is made up of a pair of magnetic cores 41 and 42 abutted and connected to each other with a magnetic gap g 3 (front gap) and a magnetic gap g 4 (back gap) in-between, as shown in Fig.10. On inclined surfaces 43a, 44a, formed by obliquely cutting the connecting surfaces of the magnetic cores 41, 42, thin magnetic metal films 47, 48 of, for example, a Fe-Al-Si alloy, are deposited from the front gap surface up to the back gap surface. These magnetic cores 41, 42 are abutted together with a gap spacer, such as SiO 2 , in-between, so that the abutment surface of the thin magnetic metal films 47, 48 affords the magnetic gaps g 3 and g 4 each having a pre-set track width. Fused glass, shown at 49, 50, 51 and 52, is charged in a molten state on the thin magnetic metal films 47, 48 and in the track width control grooves 43b, 44b. A coil winding slot 53 for placing a coil, not shown, is formed in one of the magnetic cores. With the magnetic head of the present embodiment, the medium facing surfaces of the magnetic cores 41, 42 are formed of single-crystal ferrites 43, 44, with the remaining portions of the magnetic cores being formed of poly-crystal ferrites 45, 46, respectively. The single-crystal ferrite is produced by slicing a starting ferrite block so that the medium facing surface and the abutting surface are {100} and {100} planes, respectively. The magnetic head of the present embodiment may be prepared in accordance with the method for preparing the magnetic head of the embodiment 1, using a single-crystal ferrite block and a poly-crystal ferrite block, similar to those used for the preparation of the magnetic head of the embodiment 1, as the substrates. With the magnetic head of the present embodiment, in which an inclined cut-out groove is formed in the abutment surface of the magnetic core, and the thin magnetic metal film is formed at a pre-set angle with respect to the abutment surface, with the thin magnetic metal film being abutted together to define a magnetic head, since the medium facing surface of the magnetic core is formed of single-crystal ferrite, with the remaining portion thereof being formed of poly-crystal ferrite, and the medium facing surface and the abutting surface of the magnetic core being the {100} and {100} of the single-crystal ferrite, respectively, there is little risk of abrasion due to the rubbing of the recording medium. On the other hand, the deterioration of the electro-magnetic conversion characteristics due to the crystal orientation of the ferrite is minimized, and the rubbing noise is scarcely produced, as a result of which good abrasion resistance and superior electro-magnetic conversion characteristics may be achieved. Embodiment 3 The present embodiment is directed to the MIG magnetic head in which thin magnetic metal films are formed on abutment surfaces of the magnetic cores and these thin magnetic metal films are abutted together to form a magnetic gap. The magnetic head of the present embodiment is made up of a pair of magnetic cores 61 and 62 abutted and connected to each other with a magnetic gap g 5 (front gap) and a magnetic gap g 6 (back gap) in-between, as shown in Fig.11. Meanwhile, track width suppression grooves 63, 64 for controlling the track width of the magnetic gap g 5 and track width suppression grooves 65, 66 for controlling the track width of the magnetic gap g 6 are formed in the abutment surfaces of the magnetic cores 61 and 62. There are also formed coil winding slots 69, 70. Thin magnetic metal films 77, 78 are formed on the abutment surfaces of the magnetic cores 61, 62 to follow the shape of the abutment surfaces. Fused glass is charged in molten state between the track width suppression grooves 63, 64 and the track width suppression grooves 65, 66 for connecting the magnetic cores 61 and 62 together. There is no limitation to the fused glass if it is such fused glass as is commonly employed for the manufacture of the magnetic heads. Coil winding guide slots 11, 12 are formed in the lateral sides of the magnetic cores 61 and 62, respectively. Coils, not shown, are wound across the winding slots 11, 12 and the guide slots 9, 10. With the magnetic head of the present embodiment, the medium facing surfaces of the magnetic cores 61 and 62 are formed by single-crystal ferrites 73, 74, with the remaining portions of the magnetic cores 61 and 62 being formed of poly-crystal ferrites 15, 16. The single-crystal ferrite is sliced so that the medium facing surface is the {100} plane and the abutting surface is the {100} plane. The magnetic head of the present embodiment may be prepared in accordance with the method for preparing the conventional MIG head, using a single-crystal ferrite block and a poly-crystal ferrite block, similar to those used for the preparation of the magnetic head of the embodiment 1, as the substrates. With the magnetic head of the present embodiment, in which thin magnetic metal films are formed on the abutment surfaces of the magnetic cores and the thin magnetic metal films of two magnetic cores are abutted together to define a magnetic head, since the medium facing surface of the magnetic core is formed of single-crystal ferrite, with the remaining portion thereof being formed of poly-crystal ferrite, and the medium facing surface and the abutting surface of the magnetic core being the {100} and {100} of the single-crystal ferrite, respectively, there is little risk of abrasion due to the rubbing of the recording medium. On the other hand, since the deterioration of the electro-magnetic conversion characteristics due to the crystal orientation of the ferrite is minimized and the rubbing noise is scarcely produced, good abrasion resistance and superior electro-magnetic conversion characteristics may be achieved.

Claims: A magnetic head having a pair of magnetic cores (1, 2) abutted together for defining a magnetic gap (gl) therebetween, wherein medium facing surface sides of the magnetic cores (1, 2) are formed of single-crystal ferrites and the remaining portions of the magnetic cores (1, 2) are formed of poly-crystal ferrite, characterized in that said medium facing surface sides and abutment surface sides of the magnetic cores (1, 2) are {100} planes and {100} planes of the single-crystal ferrites, respectively. The magnetic head as claimed in claim 1, wherein the magnetic metal films (77, 78) are formed on abutment surfaces of the magnetic cores (61, 62) and the magnetic gap is formed by abutting the magnetic metal films (77, 78) together. The magnetic head as claimed in claim 1, wherein a cut-out groove (43b, 44b) is formed in the abutment surfaces of the magnetic cores (41, 42) at a pre-set angle with respect to the abutment surfaces and thin magnetic metal films (47, 48) are formed in said groove (43b, 44b), said thin magnetic metal films (47, 48) being abutted together to form the magnetic gap.

Inventors: HAYAKAWA MASATOSHI, HONDA JUNICHI, IKEDA YOSHITO, ITO YOSHITOMO, KUMAGAI SEIJI, MATSUNAGA TORU, YORIZUMI MINEO, HAYAKAWA, MASATOSHI, HONDA, JUNICHI, IKEDA, YOSHITO, ITO, YOSHITOMO, KUMAGAI, SEIJI, MATSUNAGA, TORU, YORIZUMI, MINEO, HAYAKAWA, MASATOSHI, C/O SONY CORPORATION, HONDA, JUNICHI, C/O SONY CORPORATION, IKEDA, YOSHITO, C/O SONY CORPORATION, ITO, YOSHITOMO, C/O SONY CORPORATION, KUMAGAI, SEIJI, C/O SONY CORPORATION, MATSUNAGA, TORU, C/O SONY CORPORATION, YORIZUMI, MINEO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: G11B5
IPC codes: G11B5